Most electric grippers in use today are servo-driven providing them with the ability to decelerate the drive motor. The deceleration occurs in such a way that wear is limited on the drive components. This reduces the possibility of jamming the gripper members. These drives are constructed with expense motors and feedback devices, such as encoders and controllers that are complex and require significant programming. In order to reduce the cost of the electric gripper, it would be desirable to use a DC brushed motor.
The DC motor would be hard coupled to a gripper and run to a hard stop position, that is, full open/full closed or gripping the part. Here, the motor must abruptly stop when these hard stops are encountered. From an energy perspective, the system entering the hard stop position has both driving electrical energy of the motor, which provides torque to actuate the gripper, as well as kinetic energy of the drive train components moving at full speed.
The instantaneous deceleration of the hard stopping causes several mechanical problems. It causes impact loading on the gear reducer, jamming and wear of the gripper drive. Overloading the gear reducer will cause it to wear at an accelerated rate rendering it unusable over a very short period of time. Gear fracture has also been experienced in units. Some of the kinetic energy goes into jamming the device and creating wear on various drive components. Once the drive is jammed, it becomes impossible for the motor to develop enough electrical driven torque to reverse direction of the drive to unjam the mechanism. Additionally, the abrupt deceleration also has an adverse effect on the motor brushes causing electrical arcing and higher than normal wear of the brushes. This type of gripper must also be powered at all times in order to retain a part in the fingers during gripping. If current is not limited, the motor can overheat which, in turn, will decrease its life. In short, utilizing an inexpensive DC brush motor has significant drawbacks.